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Comparison of hemodynamic responses to orotracheal intubation with the GlideScope® videolaryngoscope and the Macintosh direct laryngoscope
Journal of Clinical Anesthesia (2007) 19, 245–250
Original contribution
Comparison of hemodynamic responses to orotracheal intubation with the GlideScopeR R videolaryngoscope and the Macintosh direct laryngoscope Fu S. Xue MD, FCAA (Professor)*,1 , Guo H. Zhang PhD, FCAA (Resident), Xuan Y. Li MD, FCAA (Visiting Anesthesiologist), Hai T. Sun MD, FCAA (Visiting Anesthesiologist), Ping Li PhD, FCAA (Visiting Anesthesiologist), Cheng W. Li PhD, FCAA (Visiting Anesthesiologist), Kun P. Liu MD, FCAA (Resident) Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100041, People's Republic of China Received 17 August 2006; revised 15 November 2006; accepted 15 November 2006
Keywords: GlideScope® videolaryngoscope; Macintosh direct laryngoscope; Orotracheal intubation; Hemodynamics
Abstract Study Objectives: To identify the hemodynamic responses to orotracheal intubation using a GlideScope® videolaryngoscope (GSVL) in healthy adults, and to determine whether the GSVL could attenuate the hemodynamic response to orotracheal intubation compared with the Macintosh direct laryngoscope (MDLS). Design: Randomized study. Setting: Operating room, Plastic Surgery Hospital of the Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China. Patients: 57 adult, ASA physical status I patients, scheduled for elective plastic surgery during general anesthesia requiring orotracheal intubation. Interventions: Patients were randomly allocated to either the GSVL group (n = 30) or the MDLS group (n = 27). Anesthesia was induced with intravenous injection of fentanyl 2 μg/kg, propofol 2 mg/kg, and vecuronium 0.1 mg/kg. Orotracheal intubation was started two minutes after vecuronium injection. All intubation procedures were performed by a single anesthesiologist experienced in using an MDLS and a GSVL. After intubation, anesthesia was maintained with 1% isoflurane and 60% nitrous oxide in oxygen. Measurements and Main Results: Noninvasive blood pressure (BP) and heart rate (HR) were recorded before (baseline values) and immediately after induction (postinduction values), at intubation, and for 5 minutes at one-minute intervals. Maximal BP and HR values during the observation and intubation times were also noted. The product of HR and systolic BP (ie, the rate-pressure product [RPP]) was calculated. Intubation time was significantly longer in the GSVL group than in the MDLS group (P < 0.01).
⁎ Corresponding author. Tel.: +86 010 88703936; fax: +86 010 8896 4137. E-mail address: [email protected] (F.S. Xue). 1 Fellow of the Chinese Association of Anesthesiology (FCAA). 0952-8180/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2006.11.004
246
F.S. Xue et al. Except for maximal value of diastolic BP in the GSVL group, increases in BPs during the observation in the two groups did not significantly exceed baseline values (P > 0.05). In the GSVL group, HR and RPP at intubation were significantly higher than their baseline values, and HR increase lasted for 4 minutes. In the MDLS group, HR at intubation was also significantly higher than its baseline value, but the tachycardic response lasted only for one minute. During the observation, there were no significant differences between the two groups in BP, HR, or RPP at any time points or in their maximal values. Conclusions: The hemodynamic responses to orotracheal intubation using a GSVL and a MDLS were similar. The GSVL had no special advantage over the MDLS in attenuating the hemodynamic responses to orotracheal intubation. n 2007 Elsevier Inc. All rights reserved.
1. Introduction Hemodynamic responses to laryngoscopy and tracheal intubation remain a concern. It is generally believed that various intubation devices and methods may produce different hemodynamic responses. The GlideScope® videolaryngoscope (GSVL) (Saturn Biomedical Systems, Inc, Burnaby, BC, Canada) is a novel video intubation system that provides excellent laryngeal view, it is easy and simple to operate, it causes less damage to oropharyngeal structures, and it reduces difficulty in tracheal intubation [1-5]. Although the GSVL shares similar operative techniques with the conventional Macintosh direct laryngoscope (MDLS), it can reduce the upward lifting force required to clearly expose glottis because it has a specially designed blade with a 60° curvature and is independent of the line of sight. It is suggested by the manufacturer that the upward lifting force required to expose the glottis using an MDLS is approximately 5.4 kg, but it is only 0.5 to 1.4 kg using a GSVL.2 The lesser upward lifting force helps to alleviate the stimuli to oropharyngeal structures during laryngoscopy. In addition, less neck movement is required when tracheal intubation is done with a GSVL.2 Therefore, we speculated that the GSVL is likely to attenuate the hemodynamic responses to tracheal intubation. In this study, we compared hemodynamic responses with the orotracheal intubation using a MDLS and a GSVL in healthy adult patients during general anesthesia so as to determine whether GSVL attenuated the hemodynamic responses to orotracheal intubation.
2. Materials and methods With ethics committee approval from the Plastic Surgery Hospital, Beijing, People's Republic of China, and written informed consent, 57 adults, ASA physical status I patients, scheduled for elective plastic surgery during general anesthesia requiring orotracheal intubation, were included in this study. Of these patients, 20 were men and 37 women. 2 GlideScope® Operator and Service Manual. Burnaby, BC, Canada: Saturn Biomedical Systems, Inc, 2003.
Patients ranged in age from 18 to 60 years, weighed from 45 to 90 kg, and were 150 to 180 cm tall. Patients receiving medications known to affect blood pressure (BP) or heart rate (HR), or who had predicted difficult airways, were excluded from this study. Patients were allocated by a sequence of random numbers to either the GSVL group (n = 30) or the MDLS group (n = 27). The number of samples was determined by statistical power analysis (α = 0.05, β = 0.20) after the pretest results were obtained. All patients fasted overnight and were restricted from oral intake of clear fluid for two to three hours. They all were normothermic. Midazolam 0.1 mg/kg and scopolamine 0.01 mg/kg (maximum, 0.3 mg) were given intramuscularly one hour before anesthesia. After patients entered the operating room, an intravenous (IV) cannula was inserted and noninvasive BP and HR were continuously monitored with a multifunction monitor (Datex-Ohmeda F-CU8; Datex Instrumentarium, Helsinki, Finland). Baseline BP and HR values were recorded after a stabilization period of 5 minutes. The polyvinyl chloride Murphy-type cuffed tracheal tubes (Hudson Respiratory Care Inc, Temecula, CA) with an internal diameter of 7.5 and 7.0 mm were used for male and female patients, respectively. In the GSVL group, an intubating stylet was adequately lubricated with a siliconebased fluid and inserted into the tracheal tube. The distal end of a styletted tracheal tube was bent anteriorly to an angle of 60°, which corresponded to the specially designed GSVL blade with a 60° curvature. The distal end of a styletted tracheal tube was lubricated. After a 5-minute preoxygenation period, anesthesia was induced with fentanyl 2 μg/kg, vecuronium 0.1 mg/kg, and propofol 2 mg/kg injected IV for 15 to 20 seconds. Patients were ventilated by a facemask with 100% oxygen, and orotracheal intubation was started two minutes after Table 1
Patient demographics
Gender (M/F) Age (y) Height (cm) Weight (kg)
GSVL group (n = 28)
MDLS group (n = 27)
11/17 28.2 ± 9.5 165.4 ± 6.1 61.4 ± 11.9
9/18 32.3 ± 11.0 165.1 ± 6.9 61.7 ± 13.6
Data are means ± SD except for male/female distribution.
Blood pressure, heart rate (HR), and rate pressure product (RPP) associated with orotracheal intubation
Variables
Groups Baseline values
SBP (mmHg) DBP (mmHg) MAP (mmHg) HR (bpm) RPP
GSVL MDLS GSVL MDLS GSVL MDLS GSVL MDLS GSVL MDLS
115.3 ± 114.6 ± 65.6 ± 68.7 ± 82.2 ± 84.0 ± 71.6 ± 73.8 ± 8240.8 ± 8471.4 ±
Post-ID values
At IT values
After intubation (min) 1
a
12.5 89.6 ± 15.3 109.7 ± 9.9 92.7 ± 13.6 a 106.0 ± 9.1 47.6 ± 9.6 a 66.9 ± 8.9 50.7 ± 10.4 a 67.6 ± 8.6 61.6 ± 10.7 a 81.1 ± 7.0 64.7 ± 10.5 a 80.4 ± 12.4 79.3 ± 14.6 87.5 ± 11.0 74.0 ± 11.0 80.6 ± 1614.0 7155.8 ± 2247.8 a 9833.6 ± 1540.9 6823.1 ± 1251.7 a 8493.3 ±
b
2 b
3 b
Maximal values 4
24.7 110.3 ± 20.6 98.2 ± 15.7 91.1 ± 15.8 87.9 ± 23.1 b 105.7 ± 19.7 b 96.4 ± 11.6 b 92.1 ± 10.6 a 90.0 ± 17.9 b 61.6 ± 12.1 b 53.5 ± 8.7 a, b 50.8 ± 10.0 a 46.0 ± 17.0 b 60.9 ± 10.5 b 53.3 ± 6.7 a 51.1 ± 7.8 a 49.3 ± 19.0 b 77.8 ± 13.9 b 68.4 ± 9.9 a, b 64.2 ± 11.0 a 60.0 ± 18.4 b 75.8 ± 12.8 b 67.7 ± 6.9 a, b 64.8 ± 7.6 a 62.9 ± 12.5 a, b 83.9 ± 16.7 a 83.0 ± 14.8 a 82.5 ± 14.9 a 80.4 ± 11.0 a, b 78.7 ± 9.3 b 78.2 ± 9.7 b 76.8 ± 9.7 75.9 ± 3989.1 a, b 9455.9 ± 3357.8 b 8278.1 ± 2536.3 b 7641.3 ± 2426.2 7211.1 ± 1985.3 b 8301.5 ± 1699.5 b 7533.0 ± 1261.7 a, b 7073.7 ± 1172.5 a 6827.6 ±
5 a
13.9 84.1 ± 10.2 a 88.8 ± 8.4 a 44.9 ± 8.9 a 48.9 ± 8.9 a 58.0 ± 8.1 a 62.2 ± 15.3 a 78.1 ± 11.3 73.2 ± 2473.8 6662.6 ± 1199.5 a 6486.8 ±
12.1 a 120.4 ± 9.2 a, b 113.1 ± 8.4 a 72.9 ± 9.3 a 71.0 ± 7.8 a 88.8 ± 8.5 a 85.0 ± 14.6 95.3 ± 10.6 89.0 ± 1999.6 a 11 715.6 ± 1026.6 a 10 118.2 ±
21.5 b 22.6 b 14.6 a, b 16.5 b 16.1 b 17.6 b 19.7 a, b 6.8 a, b 4217.2 a, b 2354.9 a, b
Hemodynamic responses to orotracheal intubation
Table 2
GSVL group, n = 28; MDLS group, n = 27. Data are means ± SD. GSVL = GlideScope® videolaryngoscope; MDLS = Macintosh direct laryngoscope; Post-ID = postinduction; At IT = at intubation; MAP = mean arterial pressure. a P < 0.05 compared with baseline values. b P < 0.05 compared with postinduction values.
247
248
value for the 0.05 probability level, Student's-NewmanKeuls test was used to determine which differences were significant. Quantitative data are expressed as means ± SD. A P value less than 0.05 was considered as significant and a P value less than 0.01, as highly significant.
3. Results In the MDLS group, tracheal intubation was successful on the first attempt in all 27 patients. In the GSVL group, two of 30 patients required two intubation attempts: one case failed on the first attempt because of the poor laryngeal view caused by fogging of the camera lens, and the other case failed because of difficult immobilization of the GSVL blade due to the lubricant. The two patients were excluded from statistical analysis of data. There were no significant differences in demographic data between the two groups (Table 1). Intubation time was significantly longer in the GSVL group (37.4 ± 9.9 sec) than in the MDLS group (28.4 ± 11.7 sec, P < 0.01). After anesthetic induction, BP and RPP in the two groups decreased significantly from their baseline values, but HR did not change. In the two groups, orotracheal intubation caused significant increases in BP, HR, and RPP compared with their postinduction values (P < 0.05, Table 2 and Fig. 1). Except for the maximal values of diastolic BP (DBP) in the GSVL group, BP increases during observation in the two groups did not significantly exceed their baseline values. In the GSVL group, HR and RPP at intubation were significantly higher than their baseline values (P < 0.05), and the HR increase lasted 4 minutes. In the MDLS group, HR at intubation was also significantly higher than its baseline value, but the tachycardic response lasted only one minute. In the two
14000.00 * #
12000.00
GSVL group MDLS group
#
10000.00
RPP
# * *
8000.00
* #
*
*
*
4min
5min
#
3min
#
2min
*
At Intubation
4000.00
Postinduction
6000.00
0.00
1min
2000.00 Baseline
vecuronium injection. All intubation procedures were performed by a single anesthesiologist experienced in using a MDLS and a GSVL. In the GSVL group, orotracheal intubation was performed with a technique similar to that for the conventional MDLS. The GSVL blade was inserted into the patient's mouth along the midline, gliding downward on the surface of the tongue, following the anatomical curvature of the oral cavity and pharynx, whereas the base of tongue, palate, and epiglottis all were visualized on the high-resolution liquid crystal display monitor. The tip of the GSVL blade was placed into the epiglottic vallecula and gently lifted to expose the glottis. External laryngeal compression was applied if necessary. After visualization of the glottis, a precurved styletted tracheal tube was inserted into the glottis. When the tip of the tracheal tube was advanced to the vocal cords, the intubating stylet was gently withdrawn from the tracheal tube by an assistant, and the tracheal tube advanced downward. The GSVL blade was withdrawn from the patient's mouth, and the tracheal tube was secured. In the MDLS group, a Macintosh 3 blade was used to expose the glottis in the customary manner, with the same manipulation of external laryngeal compression as used in the GSVL group, if necessary. After visualization of the glottis, a tracheal tube was inserted into the glottis during direct vision without the help of an intubating stylet. After intubation was successfully accomplished and the cuff was inflated as required, the tracheal tube was connected to the anesthesia breathing system for intermittent positive pressure ventilation. Anesthesia was maintained with 1% isoflurane and 60% nitrous oxide (N2O) in oxygen (O2). During the observation, a fresh gas flow of 1.5 L/min was used and end-tidal carbon dioxide partial pressure (PETCO2) was maintained at 35 to 40 mmHg. Inspired and end-tidal concentrations of isoflurane, O2, N2O, and CO2 were measured and displayed digitally with a multifunction monitor (Datex-Ohmeda F-CU8). BP and HR were recorded immediately after induction (postinduction values), at intubation, and every minute for the first 5 minutes after intubation. Maximal BP and HR values during the observation period were also noted. The product of HR and systolic BP (SBP), or rate-pressure product (RPP), was calculated. The intubation time, namely, the period from termination of manual ventilation using a facemask to restarting of ventilation through a tracheal tube, was recorded using a stopwatch. Patients requiring more than one attempt to achieve successful intubation were excluded from statistical analysis of data. All data were stored on a disk and analyzed with SPSS (Version 10.1; SPSS Inc, Chicago, IL) and POMS (Version 5.0; Shanghai Scientific and Technical Publishers, Shanghai, China) statistical software. Gender comparison was done via χ2 test. Comparison of general data, intubation time, and hemodynamic data between the two groups was made by unpaired Student's t test. Comparison of hemodynamic data within groups was made using repeated-measures analysis of variance. Where the calculated F value exceeded the critical
F.S. Xue et al.
After Intubation
Fig. 1 The changes in rate pressure product (RPP) associated with orotracheal intubation in the two groups. Points are means ± SD. *P < 0.05 compared with the baseline values; #P < 0.05 compared with postinduction values.
Hemodynamic responses to orotracheal intubation groups, the maximal HR and RPP values during observation were significantly higher than their baseline values (P < 0.05). Moreover, during observation, there were no significant differences between the two groups in BP, HR, or RPP at any time point or in their maximal values (Table 2 and Fig. 1).
4. Discussion The two main causes of hemodynamic responses to tracheal intubation are the stimuli to oropharyngeal structures produced by laryngoscopy and the stimuli to the larynx and trachea exerted by tracheal tube insertion. During conventional laryngoscopy, the maximal force transmitted by laryngoscope blade onto the base of tongue is said to be as high as approximately 4 to 5 kg [6]. As a result, a significant pressor and tachycardic response occurs and tends to be more intense with prolonged intubation time [6,7]. To attenuate or prevent these adverse cardiovascular responses, we have evaluated various anesthetics, intubation methods, and instruments [8]. The special blade design of the GSVL can reduce the upward lifting force required to expose the glottis during laryngoscopy,2 and it causes less mechanical stimuli to the base of tongue and the pharyngeal structures. However, in our study, the GSVL did not show any special advantages over the MDLS in attenuating the hemodynamic responses to orotracheal intubation. The reasons for our results may be multifactorial. First, as compared with a Macintosh 3 blade, the wider GSVL blade (overall thickness of 18 mm and square design of the posterior part) may increase the stimuli to the base of tongue and pharyngeal structures.2 Second, because the wider GSVL blade occupies more intraoral room and must be inserted along the midline of the mouth, the tracheal tube frequently becomes caught between the right aspect of the GSVL blade and the right distal molar. If such a problem is encountered, an additional upward lifting force is exerted so as to create enough room for the passage of a tracheal tube. This action can eliminate the advantage of the GSVL blade design. Third, when orotracheal intubation is performed with a GSVL, an intubating stylet must be used to maintain the desired curvature of a tracheal tube, which corresponded to the specially designed GSVL blade with a 60° curvature. After the tip of a precurved, styletted tracheal tube is positioned in the laryngeal aperture, the intubating stylet is withdrawn. This manipulation not only prolongs intubation time, but also causes greater stimuli to the larynx and trachea [9]. In contrast, orotracheal intubation with a MDLS is a much simpler procedure under direct vision. Fourth, because orotracheal intubation with the GSVL includes more procedures than does the MDLS, the intubation time was 24% longer in the GSVL group than in the MDLS group. Bucx et al [10] found that duration of laryngoscopy played an important role in the cardiovascular responses to tracheal intubation, whereas the laryngoscope-lifting force reduced it
249 only slightly. Finally, more and more evidence suggests that tracheal stimulus is the primary cause of the hemodynamic responses to tracheal intubation [11-13]. In orotracheal intubation with the GSVL, difficulty in downward advancement of the tracheal tube after removal of the intubating stylet often occurs. This situation results from the tracheal tube tip being snagged on the anterior wall of the upper trachea because of its anterior curvature [9]. It often requires slight rotation of the tracheal tube, withdrawal of the GSVL blade by one to two cm, or flexion of the neck so as to facilitate passage into the trachea [14,15]. It is without doubt that these manipulations can also increase the stimulus to trachea. It should be noted that, although hemodynamic variables at all time points during the study period were not significantly different between the two groups, duration of the tachycardic response was much longer in the GSVL group. This finding may be the result of the intense tracheal stimulus caused by orotracheal intubation with the GSVL. RPP is an index of myocardial O2 consumption [16], and RPP exceeding 22, 000 is commonly associated with myocardial ischemia [17]. Our results showed that although the maximal values of RPP during observation increased by 42% and 19% of their baseline values in the GSVL group and MDLS group, respectively, they did not exceed 22, 000. In conclusion, this study demonstrated that the hemodynamic responses to orotracheal intubation using a GSVL and a MDLS were similar. The GSVL had no special advantages over the MDLS in attenuating the hemodynamic responses to orotracheal intubation.
References [1] Cooper RM. Use of a new videolaryngoscope (GlideScope®) in the management of a difficult airway. Can J Anaesth 2003;50:611-3. [2] Agro F, Barzoi G, Montecchia F. Tracheal intubation using a Macintosh laryngoscope or a GlideScope® in 15 patients with cervical spine immobilization. Br J Anaesth 2003;90:705-6. [3] Doyle DJ. Awake intubation using the GlideScope® video laryngoscope: initial experience in four cases. Can J Anaesth 2004;51: 520-1. [4] Lim Y, Lim TJ, Liu EH. Ease of intubation with the GlideScope® or Macintosh laryngoscope by inexperienced operators in simulated difficult airways. Can J Anaesth 2004;51:641-2. [5] Doyle DJ. Miniaturizing the GlideScope® video laryngoscope system: a new design for enhanced portability. Can J Anaesth 2004;51:642-3. [6] Shribman AJ, Smith G, Achola KJ. Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation. Br J Anaesth 1987;59:295-9. [7] Li P, He N, Xue FS. The adverse physiologic responses to intubation and its prevention. In: Xue FS, editor. Modern airway management— critical procedure for anesthesia and intensive care. Zhengzhou: China: Zhengzhou University Publishing House; 2002. p. 1020-30. [8] Bichael JB, Bedford RF, Kil HK. Physiologic and pathophysiologic responses to intubation. In: Benumof JL, editor. Airway management: principles and practice. 1st ed. St. Louis (Mo): Mosby; 1996. p. 102-8. [9] Benumof JL. Conventional (laryngoscopic) orotracheal and nasotracheal intubation (single-lumen type). In: Benumof JL, editor. Clinical
250 procedures in anesthesia and intensive care. Philadelphia: JB Lippincott Company; 1992. p. 131. [10] Bucx MJ, van Geel RT, Scheck PA, Stijnen T. Cardiovascular effects o f f o r c e s a p p l i e d d u r i n g l a r y n g o s c o p y. A n a e st h e s i a 1992;47:1029-33. [11] Adachi YU, Takamatsu I, Watanabe K, et al. Evaluation of the cardiovascular responses to fiberoptic orotracheal intubation with television monitoring: comparison with conventional direct laryngoscopy. J Clin Anesth 2000;12:503-8. [12] Takahashi S, Mizutani T, Miyabe M, Toyooka H. Hemodynamic responses to tracheal intubation with laryngoscope versus lightwand intubating device (Trachlight) in adults with normal airway. Anesth Analg 2002;95:480-4.
F.S. Xue et al. [13] Hirabayashi Y, Hiruta M, Kawakami T, et al. Effects of lightwand (Trachlight) compared with direct laryngoscopy on circulatory responses to tracheal intubation. Br J Anaesth 1998;81:253-5. [14] Cooper RM, Pacey JA, Bishop MJ, McCluskey SA. Early clinical experience with a new videolaryngoscope (GlideScope®) in 728 patients. Can J Anaesth 2005;52:191-8. [15] Rai MR, Dering A, Verghese C. The GlideScope® system: a clinical assessment of performance. Anaesthesia 2005;60:60-4. [16] Gobel FL, Nordstrom LA, Nelson RR, Jorgensen CR, Wang Y. The ratepressure product as an index of myocardial oxygen consumption during exercise in patients with angina pectoris. Circulation 1978;57:549-56. [17] Robinson BF. Relation of heart rate and systolic blood pressure to the onset of pain in angina pectoris. Circulation 1967;35:1073-83.
Original contribution
Comparison of hemodynamic responses to orotracheal intubation with the GlideScopeR R videolaryngoscope and the Macintosh direct laryngoscope Fu S. Xue MD, FCAA (Professor)*,1 , Guo H. Zhang PhD, FCAA (Resident), Xuan Y. Li MD, FCAA (Visiting Anesthesiologist), Hai T. Sun MD, FCAA (Visiting Anesthesiologist), Ping Li PhD, FCAA (Visiting Anesthesiologist), Cheng W. Li PhD, FCAA (Visiting Anesthesiologist), Kun P. Liu MD, FCAA (Resident) Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100041, People's Republic of China Received 17 August 2006; revised 15 November 2006; accepted 15 November 2006
Keywords: GlideScope® videolaryngoscope; Macintosh direct laryngoscope; Orotracheal intubation; Hemodynamics
Abstract Study Objectives: To identify the hemodynamic responses to orotracheal intubation using a GlideScope® videolaryngoscope (GSVL) in healthy adults, and to determine whether the GSVL could attenuate the hemodynamic response to orotracheal intubation compared with the Macintosh direct laryngoscope (MDLS). Design: Randomized study. Setting: Operating room, Plastic Surgery Hospital of the Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China. Patients: 57 adult, ASA physical status I patients, scheduled for elective plastic surgery during general anesthesia requiring orotracheal intubation. Interventions: Patients were randomly allocated to either the GSVL group (n = 30) or the MDLS group (n = 27). Anesthesia was induced with intravenous injection of fentanyl 2 μg/kg, propofol 2 mg/kg, and vecuronium 0.1 mg/kg. Orotracheal intubation was started two minutes after vecuronium injection. All intubation procedures were performed by a single anesthesiologist experienced in using an MDLS and a GSVL. After intubation, anesthesia was maintained with 1% isoflurane and 60% nitrous oxide in oxygen. Measurements and Main Results: Noninvasive blood pressure (BP) and heart rate (HR) were recorded before (baseline values) and immediately after induction (postinduction values), at intubation, and for 5 minutes at one-minute intervals. Maximal BP and HR values during the observation and intubation times were also noted. The product of HR and systolic BP (ie, the rate-pressure product [RPP]) was calculated. Intubation time was significantly longer in the GSVL group than in the MDLS group (P < 0.01).
⁎ Corresponding author. Tel.: +86 010 88703936; fax: +86 010 8896 4137. E-mail address: [email protected] (F.S. Xue). 1 Fellow of the Chinese Association of Anesthesiology (FCAA). 0952-8180/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jclinane.2006.11.004
246
F.S. Xue et al. Except for maximal value of diastolic BP in the GSVL group, increases in BPs during the observation in the two groups did not significantly exceed baseline values (P > 0.05). In the GSVL group, HR and RPP at intubation were significantly higher than their baseline values, and HR increase lasted for 4 minutes. In the MDLS group, HR at intubation was also significantly higher than its baseline value, but the tachycardic response lasted only for one minute. During the observation, there were no significant differences between the two groups in BP, HR, or RPP at any time points or in their maximal values. Conclusions: The hemodynamic responses to orotracheal intubation using a GSVL and a MDLS were similar. The GSVL had no special advantage over the MDLS in attenuating the hemodynamic responses to orotracheal intubation. n 2007 Elsevier Inc. All rights reserved.
1. Introduction Hemodynamic responses to laryngoscopy and tracheal intubation remain a concern. It is generally believed that various intubation devices and methods may produce different hemodynamic responses. The GlideScope® videolaryngoscope (GSVL) (Saturn Biomedical Systems, Inc, Burnaby, BC, Canada) is a novel video intubation system that provides excellent laryngeal view, it is easy and simple to operate, it causes less damage to oropharyngeal structures, and it reduces difficulty in tracheal intubation [1-5]. Although the GSVL shares similar operative techniques with the conventional Macintosh direct laryngoscope (MDLS), it can reduce the upward lifting force required to clearly expose glottis because it has a specially designed blade with a 60° curvature and is independent of the line of sight. It is suggested by the manufacturer that the upward lifting force required to expose the glottis using an MDLS is approximately 5.4 kg, but it is only 0.5 to 1.4 kg using a GSVL.2 The lesser upward lifting force helps to alleviate the stimuli to oropharyngeal structures during laryngoscopy. In addition, less neck movement is required when tracheal intubation is done with a GSVL.2 Therefore, we speculated that the GSVL is likely to attenuate the hemodynamic responses to tracheal intubation. In this study, we compared hemodynamic responses with the orotracheal intubation using a MDLS and a GSVL in healthy adult patients during general anesthesia so as to determine whether GSVL attenuated the hemodynamic responses to orotracheal intubation.
2. Materials and methods With ethics committee approval from the Plastic Surgery Hospital, Beijing, People's Republic of China, and written informed consent, 57 adults, ASA physical status I patients, scheduled for elective plastic surgery during general anesthesia requiring orotracheal intubation, were included in this study. Of these patients, 20 were men and 37 women. 2 GlideScope® Operator and Service Manual. Burnaby, BC, Canada: Saturn Biomedical Systems, Inc, 2003.
Patients ranged in age from 18 to 60 years, weighed from 45 to 90 kg, and were 150 to 180 cm tall. Patients receiving medications known to affect blood pressure (BP) or heart rate (HR), or who had predicted difficult airways, were excluded from this study. Patients were allocated by a sequence of random numbers to either the GSVL group (n = 30) or the MDLS group (n = 27). The number of samples was determined by statistical power analysis (α = 0.05, β = 0.20) after the pretest results were obtained. All patients fasted overnight and were restricted from oral intake of clear fluid for two to three hours. They all were normothermic. Midazolam 0.1 mg/kg and scopolamine 0.01 mg/kg (maximum, 0.3 mg) were given intramuscularly one hour before anesthesia. After patients entered the operating room, an intravenous (IV) cannula was inserted and noninvasive BP and HR were continuously monitored with a multifunction monitor (Datex-Ohmeda F-CU8; Datex Instrumentarium, Helsinki, Finland). Baseline BP and HR values were recorded after a stabilization period of 5 minutes. The polyvinyl chloride Murphy-type cuffed tracheal tubes (Hudson Respiratory Care Inc, Temecula, CA) with an internal diameter of 7.5 and 7.0 mm were used for male and female patients, respectively. In the GSVL group, an intubating stylet was adequately lubricated with a siliconebased fluid and inserted into the tracheal tube. The distal end of a styletted tracheal tube was bent anteriorly to an angle of 60°, which corresponded to the specially designed GSVL blade with a 60° curvature. The distal end of a styletted tracheal tube was lubricated. After a 5-minute preoxygenation period, anesthesia was induced with fentanyl 2 μg/kg, vecuronium 0.1 mg/kg, and propofol 2 mg/kg injected IV for 15 to 20 seconds. Patients were ventilated by a facemask with 100% oxygen, and orotracheal intubation was started two minutes after Table 1
Patient demographics
Gender (M/F) Age (y) Height (cm) Weight (kg)
GSVL group (n = 28)
MDLS group (n = 27)
11/17 28.2 ± 9.5 165.4 ± 6.1 61.4 ± 11.9
9/18 32.3 ± 11.0 165.1 ± 6.9 61.7 ± 13.6
Data are means ± SD except for male/female distribution.
Blood pressure, heart rate (HR), and rate pressure product (RPP) associated with orotracheal intubation
Variables
Groups Baseline values
SBP (mmHg) DBP (mmHg) MAP (mmHg) HR (bpm) RPP
GSVL MDLS GSVL MDLS GSVL MDLS GSVL MDLS GSVL MDLS
115.3 ± 114.6 ± 65.6 ± 68.7 ± 82.2 ± 84.0 ± 71.6 ± 73.8 ± 8240.8 ± 8471.4 ±
Post-ID values
At IT values
After intubation (min) 1
a
12.5 89.6 ± 15.3 109.7 ± 9.9 92.7 ± 13.6 a 106.0 ± 9.1 47.6 ± 9.6 a 66.9 ± 8.9 50.7 ± 10.4 a 67.6 ± 8.6 61.6 ± 10.7 a 81.1 ± 7.0 64.7 ± 10.5 a 80.4 ± 12.4 79.3 ± 14.6 87.5 ± 11.0 74.0 ± 11.0 80.6 ± 1614.0 7155.8 ± 2247.8 a 9833.6 ± 1540.9 6823.1 ± 1251.7 a 8493.3 ±
b
2 b
3 b
Maximal values 4
24.7 110.3 ± 20.6 98.2 ± 15.7 91.1 ± 15.8 87.9 ± 23.1 b 105.7 ± 19.7 b 96.4 ± 11.6 b 92.1 ± 10.6 a 90.0 ± 17.9 b 61.6 ± 12.1 b 53.5 ± 8.7 a, b 50.8 ± 10.0 a 46.0 ± 17.0 b 60.9 ± 10.5 b 53.3 ± 6.7 a 51.1 ± 7.8 a 49.3 ± 19.0 b 77.8 ± 13.9 b 68.4 ± 9.9 a, b 64.2 ± 11.0 a 60.0 ± 18.4 b 75.8 ± 12.8 b 67.7 ± 6.9 a, b 64.8 ± 7.6 a 62.9 ± 12.5 a, b 83.9 ± 16.7 a 83.0 ± 14.8 a 82.5 ± 14.9 a 80.4 ± 11.0 a, b 78.7 ± 9.3 b 78.2 ± 9.7 b 76.8 ± 9.7 75.9 ± 3989.1 a, b 9455.9 ± 3357.8 b 8278.1 ± 2536.3 b 7641.3 ± 2426.2 7211.1 ± 1985.3 b 8301.5 ± 1699.5 b 7533.0 ± 1261.7 a, b 7073.7 ± 1172.5 a 6827.6 ±
5 a
13.9 84.1 ± 10.2 a 88.8 ± 8.4 a 44.9 ± 8.9 a 48.9 ± 8.9 a 58.0 ± 8.1 a 62.2 ± 15.3 a 78.1 ± 11.3 73.2 ± 2473.8 6662.6 ± 1199.5 a 6486.8 ±
12.1 a 120.4 ± 9.2 a, b 113.1 ± 8.4 a 72.9 ± 9.3 a 71.0 ± 7.8 a 88.8 ± 8.5 a 85.0 ± 14.6 95.3 ± 10.6 89.0 ± 1999.6 a 11 715.6 ± 1026.6 a 10 118.2 ±
21.5 b 22.6 b 14.6 a, b 16.5 b 16.1 b 17.6 b 19.7 a, b 6.8 a, b 4217.2 a, b 2354.9 a, b
Hemodynamic responses to orotracheal intubation
Table 2
GSVL group, n = 28; MDLS group, n = 27. Data are means ± SD. GSVL = GlideScope® videolaryngoscope; MDLS = Macintosh direct laryngoscope; Post-ID = postinduction; At IT = at intubation; MAP = mean arterial pressure. a P < 0.05 compared with baseline values. b P < 0.05 compared with postinduction values.
247
248
value for the 0.05 probability level, Student's-NewmanKeuls test was used to determine which differences were significant. Quantitative data are expressed as means ± SD. A P value less than 0.05 was considered as significant and a P value less than 0.01, as highly significant.
3. Results In the MDLS group, tracheal intubation was successful on the first attempt in all 27 patients. In the GSVL group, two of 30 patients required two intubation attempts: one case failed on the first attempt because of the poor laryngeal view caused by fogging of the camera lens, and the other case failed because of difficult immobilization of the GSVL blade due to the lubricant. The two patients were excluded from statistical analysis of data. There were no significant differences in demographic data between the two groups (Table 1). Intubation time was significantly longer in the GSVL group (37.4 ± 9.9 sec) than in the MDLS group (28.4 ± 11.7 sec, P < 0.01). After anesthetic induction, BP and RPP in the two groups decreased significantly from their baseline values, but HR did not change. In the two groups, orotracheal intubation caused significant increases in BP, HR, and RPP compared with their postinduction values (P < 0.05, Table 2 and Fig. 1). Except for the maximal values of diastolic BP (DBP) in the GSVL group, BP increases during observation in the two groups did not significantly exceed their baseline values. In the GSVL group, HR and RPP at intubation were significantly higher than their baseline values (P < 0.05), and the HR increase lasted 4 minutes. In the MDLS group, HR at intubation was also significantly higher than its baseline value, but the tachycardic response lasted only one minute. In the two
14000.00 * #
12000.00
GSVL group MDLS group
#
10000.00
RPP
# * *
8000.00
* #
*
*
*
4min
5min
#
3min
#
2min
*
At Intubation
4000.00
Postinduction
6000.00
0.00
1min
2000.00 Baseline
vecuronium injection. All intubation procedures were performed by a single anesthesiologist experienced in using a MDLS and a GSVL. In the GSVL group, orotracheal intubation was performed with a technique similar to that for the conventional MDLS. The GSVL blade was inserted into the patient's mouth along the midline, gliding downward on the surface of the tongue, following the anatomical curvature of the oral cavity and pharynx, whereas the base of tongue, palate, and epiglottis all were visualized on the high-resolution liquid crystal display monitor. The tip of the GSVL blade was placed into the epiglottic vallecula and gently lifted to expose the glottis. External laryngeal compression was applied if necessary. After visualization of the glottis, a precurved styletted tracheal tube was inserted into the glottis. When the tip of the tracheal tube was advanced to the vocal cords, the intubating stylet was gently withdrawn from the tracheal tube by an assistant, and the tracheal tube advanced downward. The GSVL blade was withdrawn from the patient's mouth, and the tracheal tube was secured. In the MDLS group, a Macintosh 3 blade was used to expose the glottis in the customary manner, with the same manipulation of external laryngeal compression as used in the GSVL group, if necessary. After visualization of the glottis, a tracheal tube was inserted into the glottis during direct vision without the help of an intubating stylet. After intubation was successfully accomplished and the cuff was inflated as required, the tracheal tube was connected to the anesthesia breathing system for intermittent positive pressure ventilation. Anesthesia was maintained with 1% isoflurane and 60% nitrous oxide (N2O) in oxygen (O2). During the observation, a fresh gas flow of 1.5 L/min was used and end-tidal carbon dioxide partial pressure (PETCO2) was maintained at 35 to 40 mmHg. Inspired and end-tidal concentrations of isoflurane, O2, N2O, and CO2 were measured and displayed digitally with a multifunction monitor (Datex-Ohmeda F-CU8). BP and HR were recorded immediately after induction (postinduction values), at intubation, and every minute for the first 5 minutes after intubation. Maximal BP and HR values during the observation period were also noted. The product of HR and systolic BP (SBP), or rate-pressure product (RPP), was calculated. The intubation time, namely, the period from termination of manual ventilation using a facemask to restarting of ventilation through a tracheal tube, was recorded using a stopwatch. Patients requiring more than one attempt to achieve successful intubation were excluded from statistical analysis of data. All data were stored on a disk and analyzed with SPSS (Version 10.1; SPSS Inc, Chicago, IL) and POMS (Version 5.0; Shanghai Scientific and Technical Publishers, Shanghai, China) statistical software. Gender comparison was done via χ2 test. Comparison of general data, intubation time, and hemodynamic data between the two groups was made by unpaired Student's t test. Comparison of hemodynamic data within groups was made using repeated-measures analysis of variance. Where the calculated F value exceeded the critical
F.S. Xue et al.
After Intubation
Fig. 1 The changes in rate pressure product (RPP) associated with orotracheal intubation in the two groups. Points are means ± SD. *P < 0.05 compared with the baseline values; #P < 0.05 compared with postinduction values.
Hemodynamic responses to orotracheal intubation groups, the maximal HR and RPP values during observation were significantly higher than their baseline values (P < 0.05). Moreover, during observation, there were no significant differences between the two groups in BP, HR, or RPP at any time point or in their maximal values (Table 2 and Fig. 1).
4. Discussion The two main causes of hemodynamic responses to tracheal intubation are the stimuli to oropharyngeal structures produced by laryngoscopy and the stimuli to the larynx and trachea exerted by tracheal tube insertion. During conventional laryngoscopy, the maximal force transmitted by laryngoscope blade onto the base of tongue is said to be as high as approximately 4 to 5 kg [6]. As a result, a significant pressor and tachycardic response occurs and tends to be more intense with prolonged intubation time [6,7]. To attenuate or prevent these adverse cardiovascular responses, we have evaluated various anesthetics, intubation methods, and instruments [8]. The special blade design of the GSVL can reduce the upward lifting force required to expose the glottis during laryngoscopy,2 and it causes less mechanical stimuli to the base of tongue and the pharyngeal structures. However, in our study, the GSVL did not show any special advantages over the MDLS in attenuating the hemodynamic responses to orotracheal intubation. The reasons for our results may be multifactorial. First, as compared with a Macintosh 3 blade, the wider GSVL blade (overall thickness of 18 mm and square design of the posterior part) may increase the stimuli to the base of tongue and pharyngeal structures.2 Second, because the wider GSVL blade occupies more intraoral room and must be inserted along the midline of the mouth, the tracheal tube frequently becomes caught between the right aspect of the GSVL blade and the right distal molar. If such a problem is encountered, an additional upward lifting force is exerted so as to create enough room for the passage of a tracheal tube. This action can eliminate the advantage of the GSVL blade design. Third, when orotracheal intubation is performed with a GSVL, an intubating stylet must be used to maintain the desired curvature of a tracheal tube, which corresponded to the specially designed GSVL blade with a 60° curvature. After the tip of a precurved, styletted tracheal tube is positioned in the laryngeal aperture, the intubating stylet is withdrawn. This manipulation not only prolongs intubation time, but also causes greater stimuli to the larynx and trachea [9]. In contrast, orotracheal intubation with a MDLS is a much simpler procedure under direct vision. Fourth, because orotracheal intubation with the GSVL includes more procedures than does the MDLS, the intubation time was 24% longer in the GSVL group than in the MDLS group. Bucx et al [10] found that duration of laryngoscopy played an important role in the cardiovascular responses to tracheal intubation, whereas the laryngoscope-lifting force reduced it
249 only slightly. Finally, more and more evidence suggests that tracheal stimulus is the primary cause of the hemodynamic responses to tracheal intubation [11-13]. In orotracheal intubation with the GSVL, difficulty in downward advancement of the tracheal tube after removal of the intubating stylet often occurs. This situation results from the tracheal tube tip being snagged on the anterior wall of the upper trachea because of its anterior curvature [9]. It often requires slight rotation of the tracheal tube, withdrawal of the GSVL blade by one to two cm, or flexion of the neck so as to facilitate passage into the trachea [14,15]. It is without doubt that these manipulations can also increase the stimulus to trachea. It should be noted that, although hemodynamic variables at all time points during the study period were not significantly different between the two groups, duration of the tachycardic response was much longer in the GSVL group. This finding may be the result of the intense tracheal stimulus caused by orotracheal intubation with the GSVL. RPP is an index of myocardial O2 consumption [16], and RPP exceeding 22, 000 is commonly associated with myocardial ischemia [17]. Our results showed that although the maximal values of RPP during observation increased by 42% and 19% of their baseline values in the GSVL group and MDLS group, respectively, they did not exceed 22, 000. In conclusion, this study demonstrated that the hemodynamic responses to orotracheal intubation using a GSVL and a MDLS were similar. The GSVL had no special advantages over the MDLS in attenuating the hemodynamic responses to orotracheal intubation.
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